1. Field of the Invention
The present invention relates to an internal combustion engine to be mounted on automobiles or the like.
2. Description of the Related Art
Recently, regarding internal combustion engines to be mounted on automobiles or the like, there has been proposed a technique according to which a combustion heater, a rapid heater or the like is provided in order, for example, to improve the performance of the room heating device when the engine is in the cold state or to promote the warming-up of the internal combustion engine.
Known examples of the above-mentioned technique include “an internal combustion engine having a combustion heater” as disclosed in JAPANESE PATENT LAID-OPEN PUBLICATION NO. 2000-240519A, “an internal combustion engine having a lean NOx catalyst” as disclosed in JAPANESE PATENT LAID-OPEN PUBLICATION NO. 2000-186531A, “an internal combustion engine having a lean NOx catalyst” as disclosed in JAPANESE PATENT LAID-OPEN PUBLICATION NO. 2000-186531A, JAPANESE PATENT LAID-OPEN PUBLICATION NO. 2000-186532A, and JAPANESE PATENT LAID-OPEN PUBLICATION NO. 2000-186534A, and “a control device for a rapid heater” as disclosed in JAPANESE PATENT PUBLICATION(POST-EXAMINATION) NO. 5-81445B.
The internal combustion engine having a combustion engine disclosed in JAPANESE PATENT LAID-OPEN PUBLICATION NO. 2000-240519A is equipped with a combustion heater which raises the intake temperature of the internal combustion engine by introducing combustion gas generated through combustion of fuel into the intake passage of the internal combustion engine; at the time of cranking of the internal combustion engine, the quantity of heat of the combustion gas supplied from the combustion heater to the intake system is controlled by using the intake air temperature, outside-air temperature, engine temperature, etc. as parameters, whereby the in-cylinder temperature at the top dead center of the compression stroke is adjusted to a desired temperature, thereby improving the startability of the internal combustion engine.
The internal combustion engine having a lean NOx catalyst as disclosed in JAPANESE PATENT LAID-OPEN PUBLICATION NO. 2000-186531A and JAPANESE PATENT LAID-OPEN PUBLICATION NO. 2000-186534A is equipped with a combustion heater which raises the temperature of the lean NOx catalyst by introducing combustion gas generated through combustion of fuel into an exhaust passage on the upstream side of the lean NOx catalyst; when it is necessary to reduce nitrogen oxide (NOx) with the lean NOx catalyst, when it is necessary to eliminate sulfur poisoning of the lean NOx catalyst, or when it is necessary to remove exhaust particulate matters (PM) accumulated on the lean NOx catalyst, the combustion heater is operated at rich air-fuel ratio, whereby the surplus fuel component not used for combustion in the combustion heater is supplied to the lean NOx catalyst as a reducing agent.
The internal combustion engine having a lean NOx catalyst as disclosed in JAPANESE PATENT LAID-OPEN PUBLICATION NO. 2000-186532A is equipped with a combustion heater which raises the temperature of the lean NOx catalyst by introducing combustion gas generated through combustion of fuel into an exhaust passage on the upstream side of the NOx catalyst, and a mechanism which supplies a reducing agent to the lean NOx catalyst; the combustion gas of the combustion heater heats the lean NOx catalyst to a desired temperature range, and a reducing agent is supplied from the reducing agent supply mechanism to the NOx catalyst, whereby reduction of nitrogen oxide (NOx), elimination of sulfur poisoning, and removal of exhaust particulate matters are effected on the lean NOx catalyst.
In the control device for a rapid heater as disclosed in JAPANESE PATENT PUBLICATION(POST-EXAMINATION) NO. 5-81445B, a rapid heating burner composed of a vaporizing glow plug and an ignition glow plug is arranged in the intake pipe of the internal combustion engine, and a heat exchanger for effecting heat exchange between the combustion gas discharged from the rapid heating burner and the room heating air is arranged in the intake pipe on the downstream side of the rapid heating burner; when the internal combustion engine is cold-started, the high temperature gas generated through by the rapid burner is introduced into the intake air.
Since the combustion heater and the rapid heating burner are capable of highly efficient combustion, in other words, a combustion akin to complete combustion, the combustion gas discharged from the combustion heater or the rapid heating burner contains a small amount of oxygen and a large amount of carbon dioxide.
Thus, as in the case of the internal combustion engine having a combustion heater as disclosed in JAPANESE PATENT LAID-OPEN PUBLICATION NO. 2000-240519A and the control device for a rapid heater as disclosed in JAPANESE PATENT PUBLICATION (POST-EXAMINATION) NO. 5-81445B, when the combustion gas of the combustion heater or the rapid heating burner is supplied to the intake system at the start of the internal combustion engine, it is possible to raise the intake air temperature of the internal combustion engine with the heat of the combustion gas; however, a reduction in the amount of oxygen taken in the internal combustion engine involves an increase in the amount of carbon dioxide, so that the ignitionability and combustion stability of the fuel in the internal combustion engine are impaired, with the result that the startability of the internal combustion engine may deteriorate.
As in the case of the internal combustion engine having a lean NOx catalyst as disclosed in JAPANESE PATENT LAID-OPEN PUBLICATION NO. 2000-186531A and JAPANESE PATENT LAID-OPEN PUBLICATION NO. 2000-186534A, when the combustion heater is operated at a rich air-fuel ratio, soot is accumulated in the combustion heater, which may lead to a deterioration in the performance of the combustion heater. Further, when the combustion heater is operated at rich air-fuel ratio in order to supply reducing agent to the lean NOx catalyst, the surplus fuel component not used for the combustion in the combustion heater is supplied to the lean NOx catalyst as a reducing agent, which means waste of fuel for combustion in the combustion heater.
As in the case of the internal combustion engine having a lean NOx catalyst disclosed in JAPANESE PATENT LAID-OPEN PUBLICATION NO. 2000-186532A, when a reducing agent supply mechanism is provided in addition to the combustion heater, the internal combustion engine becomes rather hard to be mounted in a vehicle.